Communication through videoconferencing has grown significantly in recent years due to the rapid development of network services and video compression techniques. In fact, videoconferencing applications are now widely used on personal computers as well as dedicated videoconferencing terminals. In videoconferencing, the image quality is not only determined by the available network bandwidth and applied video compression techniques, but it is also significantly influenced by the illumination condition. Unsatisfactory illumination conditions may lead to underexposure or overexposure of the area of interest, such as a human face.
FIGS. 1A and 1B illustrate an underexposed face 101 and an overexposed face 103, respectively, with conventional video image processing. Of these two typical cases, image 101 of the underexposed face represents scenes that possess a bright background. In image 101, the face area is underexposed because the camera's exposure level is influenced by the bright background. On the other hand, image 103 of the overexposed face represents scenes that posses a dark background, which also adversely affects the performance of conventional automatic exposure adjustments. Thus, a bright background can cause a face to appear too dark (e.g., as in underexposed face 101), and a dark background can cause a face to appear too bright (e.g., as in overexposed face 103).
Although most videoconferencing equipment, such as personal computer digital cameras, can automatically adjust the exposure level according to the illumination condition, they cannot identify the area of interest in a video image. Consequently, the automatically-adjusted exposure level may be unsatisfactory or even poor in the area of interest. With video images for videoconferencing applications, the area of interest is often a human face. When the human face is obscured due to a poor exposure level, much of the additional nonverbal communication offered by videoconferencing is unfortunately comprised.
Accordingly, there is a need for schemes and/or techniques that can efficiently improve the exposure level and/or clarity of an area of interest in video images.